Ashing is a term often used by dark skin consumers to describe the dull, grayish appearance of their skin condition. Skin ashing is related to the overall white/grayish appearance of the skin caused by scattering of the uplifted corneocytes. The uplifted corneocytes that characterize ashing skin increase the diffuse scattering and reduce the reflection of light on the skin surface. As a result, the upper layers of stratum lose translucency and become opaque and dull.
The contrast of whiteness caused by the uplifted corneocytes on the skin surface can be greatly enhanced relative to darker skin by using a cross-polarized imaging technique. Specifically, this is done by suppressing the Fresnel Reflection contribution on the skin. Images obtained using a cross-polarized imaging method have been found very useful for quantifying skin ashing since the glare from Fresnel Reflection can severely influence the whiteness appearance of skin. By suppressing the Fresnel Reflection, the white ashing can therefore be seen more clearly.
Polarizers are used widely in photography to reduce glare. J. Philip (J. Soc. Cosmet. Chem., 39, 121, 1988), for example, discloses polarizers to reduce glare and get more sub-surface (e.g., viable epidermis and dermis in contrast to stratum corneum) information for images of skin. Philip used cross-polarization for improving optical discrimination of skin. However, Philip fails to teach or suggest use of cross-polarization as part of a process to measure skin ashing as described in the subject invention. More specifically, and as noted above, the technique he uses is for telangis (dermal) and age spots (viable dermis) rather than for measuring information on the stratum corneum such as is done in the subject invention where ashing is measured.
U.S. Pat. No. 5,198,875 to Bazin et al. describes a device that is designed to assess the brightness of a surface, more particularly of the skin. A device for measuring the brightness of the skin surface, using light-sensitive photo detectors at both parallel-polarized and cross-polarized conditions is described. Using this device, spectral brightness can be assessed by the parallel polarization results, and diffuse brightness can be assessed by the cross-polarized results. Therefore, Bazin et al. does not take an image of the skin and clearly fails to teach or suggest a method of measuring skin ashing.
No process for first acquiring an image and then using the image to quantify the amount of skin ashing is found in this or any prior art as far as applicants are aware.
Unexpectedly, applicants have now discovered that, using cross-polarized imaging, it is possible to quantify the degree of skin ashing.